Summertime Indirect DHW Eff?

Mark Adams

..of the small Ultra is 16-80 MBH input. My 4 zones would be DHW, 1/2 of first floor (20,000), other half of first floor (15,000) and bsmt (10,000) for those times is needs heat which will not be often.

Thanks,
Mark

Mark Adams

Been wondering..

what the efficiency of making indirect DHW might be in the summer when it is the only load on a boiler (3 people with fairly normal water use, no exceptional high flow shower heads and just a standard sized tub). Could eff be so low that one might be better off with a regular power vent fired tank with a good warranty?

I'm still undecided between a standard sealed combustion boiler, single stage condenser and modulating boiler for my system. Back when I was going FHA on my newbuild I had it slated for a B-W 48Gal, EF=0.62 gas fired tank.

TIA,

Mark

Mark Eatherton1

Absolutely...

NO way a direct fired tank is more efficient than an indirect fired tank. Especially if you go the Euro route with a fully modulating, condensing boiler.

I used to have a tankless in my house. Virtually ENDLESS supply of hot water, and NO standby loss. Since installing my Posidon tank and condensing Munchkin, I've reduced my fuel consumption by an additional 10% with no change in loading.

Beat that!

ME

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Mark Eatherton1

PS...

Before I had the tankless, I had a conventional direct fired tank. When comparing the fuel use between those two, my fuel comsumption dropped by 30%, so 30 + 10 = 40% savings for DHW using the ultimate versus a REAL DOG.

It's WORTH the investment.

ME

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Ron Schroeder

When I moved in, I had a tankless coil in my boiler. Oil usage in the summer wasn't all that much less than winter and the basement was HOT.

Now with an indirect, my summer time usage went down by more than a factor of 4. After changing the aquastat on the indirect with a Tekmar 150 with the differential set to 40 degrees and the tank going from 170 down to 130 (and a tempering valve on the DHW output) before the next call for heat the fuel usage is even lower. I cold start the boiler in the summer and sometimes it is several days between boiler firing.

Ron

Mark Adams

So you're saying..

that your have your own Posiden Adventure! Cool.

My **REAL** issue is that my home design load is about 33,000 BTU/hr (and will be even less now that we've changed to Pella Designer windows with U=0.25 from 0.35) and my hot water needs to have 50,000 BTU/hr +/-.

I know that this screams for a modulating boiler. I know this makes control easier too. It is easy to simply use fixed mixing for the rad panels and radiant loops and let these loops ride the OD reset curve along with the BB. Much of the home will be HWBB. (The budget axe has to fall somewhere.)

BUT, the engineer in me says, KISS. Go with a fixed output unit, get a much longer service life, pay less now and more in energy bills to run it for that longer life. The OTHER engineer in my head says to get the modulator, let is die in 2020 and then buy the solar nuclear fusion hydronomator which will heat the house and provide wireless electricity to boot!

Best regards,

Mark

Mark Hunt

The Buderus G142


can solve that issue. It allows you to derate the boiler for heating while keeping full fire available for domestic water production.

We have just such an application in a home we did recently. The floor warming and radiant loads only required a small percentage of the boilers actual capacity but the domestic water load required most of the available output. With the turn of a dial we derated the heating load side to 40% of capacity but on a call for domestic the boiler revs up to full capacity. We used a Buderus indirect for the domestic water production.

As others have said, an indirect tank is far more efficient than any direct-fired storage unit.

Hope this helps!

Mark H

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Floyd_8

The Ultra..

will also provide separate output ranges..... I have my Ultra backed down to a little over half fire max. for heating and it fires full 155,000 for the DHW. If it were me I'd be going modulating and scrap the boiler for the super duper hydronuker thing-ama-bobber that will be making heat and hot water at about 200% eff. as today's efficiencies go.....in 2020...
I took out a regular 40 gas hot water heater and installed and indirect with the Ultra.... dropped the summertime gas bill to almost exactly half..... go indirect...

Floyd

Mark Adams

The G142

sounds neat Mark. I only took a brief look at these because the local Buderus dealer gave me outrageously high prices for hydronics. As did others. Seems that until you get to exact specs, most guys quote very high due to the variables of hydronics. The HVAC I'm going with does to Dunkirk so the Ultra is on the table.

Thanks,
Mark

Mark Adams

Floyd,

as I mentioned, my heating load is going to be 30-35K tops. And only having 3 people in the house I can go with a smallish boiler. I'll recheck the Ultra specs. Thanks.

Mark

Floyd_8

You could use

the Ultra 80... with a 30 or 40 plus you would still have plenty of hot H2O and be able to easliy back the boilerfiring rate down to 35,000.
My experience with the boiler also shows me that the eff. runs higher when the boiler is limited to half fire or less, no matter what temp. the boiler is running at. You will also find that most of the time when the boiler is making hot H2O that the boiler will be running at half fire or less, also. However you will still have the full fire there if needed.

Floyd

bob_34

tank vs. indirect

IF you have small zone loads of heat and you upgrade the size of the boiler to accomodate an indirect domestic load, you may be loosing out a little on one of the biggest features of the Ultra- the 20% sipping factor for the shoulder months. with a bigger boiler accomodating the indirect the 20% becomes a bigger gas load when trying to sip the smallest zone. doesn,t matter if your smallest zone is more than the 20% sipping. just a thought.

ALH_3

Fuel Usage

Maybe if you have a very large heating load and a very small DHW load. The biggest concern would be the fuel to heat up a cast iron heat exchanger and the fluid in the boiler. If you're using a low mass boiler, such as a vitodens, ultra, munchkin, or other, you have overcome that loss. Even with a small cast iron boiler, it's less of an issue. If this was a large commercial building with virtually no DHW load, that's a different story.

As ME said, it's worth the investment. You're better off using the boiler and indirect instead of a gas water heater in my opinion.

-Andrew